In some applications, it is preferred that the viscosity of an epoxy curing agent not change fundamentally for an extended period of time after combining an epoxide and a curing agent. Such a combination can facilitate the next step according to the intended use, such as coating, lamination, injection, potting or impregnation of composite compositions which contain reinforced or non-reinforced components.
When a combination of an epoxide component and a polyamine-based curing agent is left standing for a long period of time, a reaction can occur and the viscosity of the composition increases. Thus, the composition has a maximum time during which the composition can be used, such as coating, lamination, injection, potting or impregnation. The period of time beginning from combining the composition and ending when the viscosity increases of the combination is no longer capable of performing the desired working procedure, is referred to as “pot life”, or working life. In many applications, a longer pot life is a desirable property to aid processing flexibility.
It is known in this art that a mixed composition comprising a solid epoxide component and similarly a solid curing agent component are known to have a long pot life (or shelf life). This is because the initiation of curing is depending on the thermal fusion of two components. Further, a large number of semi liquid-type compositions obtained by dispersing a solid curing agent component in a liquid epoxide component are known and also in this case, since the curing agent component is a solid, the initiation of curing is dependent on thermal fusion of the curing agent component or mixing of two components due to mutual dissolution.
However, compositions containing solids have a drawback ascribable to the fact that at least one component is a solid. More specifically, in the case of a composite material, for example, a fiber reinforced composite comprising resin binders and fibers, the resin binder needs to penetrate into a fiber bundle, but when a solid component is used, a filtration phenomenon by the fiber occurs thereby causing separation between binder components and, as a result, a curing failure may be brought about. The same applies to the case of using a woven fabric or the like for the reinforcing material. For this reason, a liquid epoxide component and a liquid curing agent component would be desirable as a material capable of overcoming such a problem.
Another drawback in known compositions is that these compositions have a relatively short pot life. Generally, in a composition having a short pot life, a reaction abruptly occurs and the time to reach the cured state is short, whereas in a composition having a long pot life, the time necessary for curing is long. As a result, there is a need in this art for a liquid epoxide-based composition having as long a pot life as several tens of hours, being curable at relatively low temperature range (moderate temperature range) of 100° C. or less.
Such a composition comprising an epoxide and curing agent both being a liquid would enable paint coating for the purpose of protecting the inner surface of a water supply pipe, a sewer pipe, gas supply pipes or other industrial liquid transport pipes, or other outdoor construction for the purpose of, for example, laminating a protective lining or the like serving also as pipe reinforcement, by using an organic or in organic fiber or film or the like. In particular, the composition would be useful for rehabilitation work or the like of the inner surface of a pipe, which is performed without digging up fluid transport pipes already buried under the ground.
The rehabilitation work of these buried pipes is usually performed by setting the section between a manhole and a manhole as one unit of work. The working procedure comprises, in sequence, mechanical removal of old coating remaining inside of the pipe, washing with water, drying, coating of a resin component, spreading of inverted fibers or films by using hot air or hot water, and maintenance of a given temperature with hot water or hot air. When conducting a rehabilitation using a fiber or a film, in the case of a short work selection, coating of a binder or primer onto the inside of the pipe and lamination by spreading of inverted cylindrical fiber or films may be performed even if the pot life of the composition is short, but in the case of a long work selection, a long time over several tens of hours is necessary.
For rehabilitation of pipes used for transporting water or other fluid media, there is a need in this art for composite system which can be applied to the inside steel or concrete wall of such pipes. Known compositions cannot provide appropriate working time (pot life), cause odor or toxicity issues from employed chemicals (e.g., mercaptan, acrylonitrile, and isocyanates) in binders or cannot be applied to multi layer and non-transparent films/composites due to the curing process (e.g. UV cure).
US Patent Pub No 2010/0227981A1 discloses a composition comprising at least one phenyl glycidyl ether polyepoxide having at least one epoxide group of oxirane structure in the molecule; and a curing agent component comprising one salt compound formed from an N-alkanol piperidine and a carboxylic acid which can be used in the rehabilitation of water pipes at a cure temperature of less than 100° C. and specifically at 80° C.
The disclosure of the previously identified patents and patent applications are hereby incorporated by reference.